1. Field of the Invention
The present invention relates to a low optical loss, highly crosslinked and all polymer process compatible fluorinated maleimide based optical polymer system. The invention also relates to methods of making such polymers and single or multi-mode polymer waveguide structures fabricated by photolithography, hot-embossing and UV curing of the materials.
2. Description of the Related Art
The microelectronic and optical industries rely on hundreds of polymeric materials. Polymeric material currently play an important role in, for example, photonic devices coating materials, and electro-optical devices.
The high speed and high capacity data transmission of the internet makes it possible for everyone to communicate to the world simply through their fingers. With the explosive increased demand for information exchange, there is also a tremendous market driving force pushing all the communication units to their lowest possible price. The future information highway is expected to have an all-optical interconnection because of its great potential to reduce the cost. The application of polymer interconnection in the micro-optical industry has been attracting great attention because of a significant potential cost-savings from various convenient polymer processes. The mass production of polymer components from micro-photolithographic processes and micro hot-embossing processes are a few areas needing to be addressed. So far, many polymer based optical devices have been demonstrated such as polymer waveguides, polymer optical couplers, polymer optical power splitters, polymer wavelength switches, polymer wavelength bragg filters, polymer thermal optical attenuators and polymer planar amplifiers etc. See, for example, Brauer et al., xe2x80x9cPolymer for Passive and Switching Waveguide Components for Optical Communicationxe2x80x9d SPIE Critical Reviews, vol. CR63 (1996) and Elada et al., xe2x80x9cNext Generation Polymer Photonic Devices in Sol-Gel and Polymer Photonic Devicesxe2x80x9d SPIE Critical Reviews Vol. CR 68 (1997). However, from a material and process point of view, there are several issues that limit the polymeric materials that can be used. One is the relatively high optical loss at the near IR region because of the Cxe2x80x94H overtone absorption. The second problem is the thermal and environmental stability of polymers compared to the existing competitive inorganic based silicate materials. Also, the polymer microfabrication process itself significantly narrows down the choice of optical polymers. For example, the photolithography process limits the selection of polymers to organic solvent or alkaline solvent soluble hydrocarbon photoresists. This creates an optical loss issue. The hot embossing process is applicable only to thermoplastic polymers. This creates a thermal stability problem from the large coefficient of thermal expansion (CTE).
The microlithographic process, a powerful process to manufacture millions of computer chips, is the xe2x80x9cworkhorsexe2x80x9d of the current microelectronic industry. Seeking the advantages of polymer microfabrication process in optical communication industry, a low optical loss photoresist could be one of the smartest choices for fabricating the micro-optical components because the same production line at the semiconductor industry could be directly applied. Logically, it is easy to realize that a crosslinkable negative photoresist must be a better candidate because of good thermal stability in contrast with many linear positive photoresist resins. The problem is that most organic photoresists are hydrocarbon polymers which have a very high optical loss. On the other hand, fluorinated photoresists may have lower optical loss but are hardly soluble in common organic solvents and have to be processed in supercritical carbon dioxide. Most recently, Hult et al., xe2x80x9cLow-Loss Passive Optical Waveguides Based on Photosensitive Poly(pentafluorostyrene-co-glycidyl methacrylate)xe2x80x9d Macromolecules, vol. 32 pages 2903 (1999), developed a fluorine containing copolymer, poly-(pentafluorostyrene-coglycidyl methacrylate), to fabricate the low loss optical waveguides based on the photosensitive reaction. These polymer waveguides have a higher refractive index (xcx9c1.48 at 1550 nm) than silica (1.44 at 1550 nm) and low glass transition temperature ( less than 100xc2x0 C.) even after the crosslink reaction.
An alternative process is to utilize a traditional plastic polymer structure formation process such as hot-embossing or injection molding. However, the inherent higher coefficient of thermal expansion (CTE) of plastic polymers (100-300 ppm) makes it near impossible to meet requirements for optical devices. It is also difficult for these polymers to pass other harsh environmental tests such as exposure to 85% relative humidity and 85xc2x0 C.
Thus, there is a need for a polymeric material which has a low optical loss, has a low coefficient of thermal expansion and is capable of processing by UV curing, photolithography, and hot embossing as well as other polymeric processes to produce optical devices.
According to an embodiment of the present invention, there is provided a terpolymer containing N-halogenated phenyl maleimide units or phenyl bismaleimide units (I), one or more second units (II) selected from the group consisting of halogenated acrylates, halogenated styrenes, halogenated vinyl ethers, halogenated olefins, halogenated vinyl isocyanates, halogenated N-vinyl amides, halogenated allyls, halogenated propenyl ethers, halogenated methacrylates, halogenated maleates, halogenated itaconates, and halogenated crotonates and one or more third units (III) comprising a monomer containing both a free radically polymerizable group and a cationic ring opening polymerizable group. This terpolymer is prepared by radical polymerization.
Also, in accordance with another embodiment of the invention, there is provided an optical device, formed via one or more polymer processing steps of a terpolymer containing N-halogenated phenyl maleimide units or phenyl bismaleimide units (I), one or more second units (II) selected from the group consisting of halogenated acrylates, halogenated styrenes, halogenated vinyl ethers, halogenated olefins, halogenated vinyl isocyanates, halogenated N-vinyl amides, halogenated allyls, halogenated propenyl ethers, halogenated methacrylates, halogenated maleates, halogenated itaconates, and halogenated crotonates and one or more third units (III) comprising a monomer containing both a free radically polymerizable group and a cationic ring opening polymerizable group. The terpolymer is prepared by radical polymerization. The polymer processing steps are selected from the group consisting of micro-photolithography, micro hot-embossing, micro-molding, spin-molding, UV curing, injection molding and spin-coating.
The invention provides polymers useful in processes for producing optical devices that overcome one or more of the deficiencies, such as those discussed above, of currently used polymers. It also provides methods of making terpolymers and using such polymers to produce optical devices.
Additional, features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.